The present invention relates to a photosensitive polyimide precursor. More particularly, the invention relates to a photosensitive polyimide precursor capable of producing a polyimide resin having high heat resistance and high photosensitivity.
Having the properties required for electronic material such as heat resistance, insulating property, adhesiveness, etc., polyimide resins are used in the field of semiconductor industry as a substitute for inorganic materials, for example, as a structural material for hydrid high-density printed circuit boards.
Especially, attention is given to photosensitive polyimide resins because of their potencies for enabling remarkable simplification of the semiconductor production process and flattening of the pattern in addition to their possession of specific properties of polyimide. The photosensitive polyimide resins now available, however, are not always satisfactory in photosensitivity.
The present invention provides a photosensitive polyimide precursor used for interlayer insultating films, surface protective films, etc., which precursor has a sufficient photosensitivity for use as a starting material for the production of semiconductors and enables formation of a fine pattern, and which, by a heat treatment, can be made into a polyimide resin having excellent heat resistance.
The conventional polyimide type photosensitive polymers can be roughly classified into two types: the polyimides having photosensitive groups in the side chain and the polyimides having photosensitive groups in the main chain.
The former type of polymers, that is, those having photosensitive groups in the side chain, are disclosed, for instance, in Japanese Patent Kokai (Laid-Open) Nos. 116216/79, 116217/79, 145794/79, 9510/80, 9538/80, 45746/80, 45748/80 and 143329/82. These polymers are subject to a loss of photosensitive groups in the course of heat treatment for cyclization, resulting in a marked decrease in thickness of the formed film. Also, these polymers are not always satisfactory in photosensitivity. Thus, this type of polymers present problems in practical use thereof.
The latter type of polymers, or those having photosensitive groups in the main chain, are free from scattering loss of photosensitive groups in the heat treatment for cyclization. In Japanese Patent Kokai (Laid-Open) No. 131227/82, for instance, there is disclosed an imide resin having as its diamine component a diamine represented by the following general formula (III): EQU H.sub.2 N--R.sub.1 --CH.dbd.CH--R.sub.2 --NH.sub.2 (III)
wherein R.sub.1 and R.sub.2 represent independently a divalent aromatic or aliphatic group. Also, Japanese Patent Kokai (Laid-Open) No. 145216/84 discloses a polyamideimide resin prepared by using a diamine represented by the following general formula (IV) as diamine component: ##STR2##
Both of these polymers are characteristically soluble in organic solvents. However, the polymer proposed in Japanese Patent Kokai No. 131227/82 is in the range of 310.degree.-380.degree. C. in thermal decomposition temperature and has a photosensitivity of only about 5 J/cm.sup.2, while the polymer proposed in Japanese Patent Kokai No. 145216/84, although higher than 400.degree. C. in thermal decomposition temperature, is less than 3.5 J/cm.sup.2 in photosensitivity. Thus, both of them are unsatisfactory for practical use.